Field of the Invention
The invention relates to a method and apparatus for regulating web tension in a web-fed rotary offset printing press.
Apparatuses and methods for regulating web tension in web-fed rotary offset printing presses have become known heretofore from the prior art and are used to compensate for changes in web tension of the type, which occur during a printing operation.
The German published, nonprosecuted Patent Application (DE-OS) 37 31 214 describes a device for the controlled feeding of web material to printing presses, as well as an appertaining method, with which the deflection of a compensating roller engaging with the running web is measured, and the signal is used to regulate the rotational speed of a pair of tension rollers cooperating with the web. A pneumatic cylinder which actuates the compensating roller is acted upon with constant pressure from a compressed air container connected to a compressed air source, a digital valve being provided between the compressed air source and the compressed air container so as to be able to adjust the pressure and thus the tensile stress of the web to various values. This publication provides no suggestion whatsoever to a person skilled in the art of how to regulate the tensile stress of the web in accordance with or as a function of the web speed.
As has been shown, the first time a web-fed rotary offset printing press is run up to operating speed with a newly inserted web of paper, the problem often occurs that the web will tear or break due to changes in the tensile stress of the web, the causes for which are often ascertainable only with difficulty, the web tears or breaks not only causing a decrease in production but often also damaging parts of the printing presses.